/*********************************************************************
* Filename:   sha256.c
* Author:     Brad Conte (brad AT bradconte.com)
* Copyright:
* Disclaimer: This code is presented "as is" without any guarantees.
* Details:    Implementation of the SHA-256 hashing algorithm.
              SHA-256 is one of the three algorithms in the SHA2
              specification. The others, SHA-384 and SHA-512, are not
              offered in this implementation.
              Algorithm specification can be found here:
              * http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf
              This implementation uses little endian byte order.
*********************************************************************/

/*************************** HEADER FILES ***************************/
#include <memory.h>
#include "sha256.h"

/****************************** MACROS ******************************/
#define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
#define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))

#define CH(x,y,z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) (ROTRIGHT(x,2) ^ ROTRIGHT(x,13) ^ ROTRIGHT(x,22))
#define EP1(x) (ROTRIGHT(x,6) ^ ROTRIGHT(x,11) ^ ROTRIGHT(x,25))
#define SIG0(x) (ROTRIGHT(x,7) ^ ROTRIGHT(x,18) ^ ((x) >> 3))
#define SIG1(x) (ROTRIGHT(x,17) ^ ROTRIGHT(x,19) ^ ((x) >> 10))

/**************************** VARIABLES *****************************/
static const uint32_t k[64] =
{
    0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
    0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
    0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
    0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
    0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
    0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
    0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
    0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
};

/*********************** FUNCTION DEFINITIONS ***********************/
inline uint32_t bswap_32(uint32_t x)
{
    return (((x & 0xff000000U) >> 24) | ((x & 0x00ff0000U) >> 8) |
        ((x & 0x0000ff00U) << 8) | ((x & 0x000000ffU) << 24));
}

void static inline WriteBE32(unsigned char* ptr, uint32_t x)
{
    *(uint32_t*)ptr = bswap_32(x);
}

static void sha256_transform(SHA256_CTX *ctx, const uint8_t data[])
{
    uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

    for(i = 0, j = 0; i < 16; ++i, j += 4)
    {
        m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
    }
    for(; i < 64; ++i)
    {
        m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
    }

    a = ctx->state[0];
    b = ctx->state[1];
    c = ctx->state[2];
    d = ctx->state[3];
    e = ctx->state[4];
    f = ctx->state[5];
    g = ctx->state[6];
    h = ctx->state[7];

    for(i = 0; i < 64; ++i)
    {
        t1 = h + EP1(e) + CH(e, f, g) + k[i] + m[i];
        t2 = EP0(a) + MAJ(a, b, c);
        h = g;
        g = f;
        f = e;
        e = d + t1;
        d = c;
        c = b;
        b = a;
        a = t1 + t2;
    }

    ctx->state[0] += a;
    ctx->state[1] += b;
    ctx->state[2] += c;
    ctx->state[3] += d;
    ctx->state[4] += e;
    ctx->state[5] += f;
    ctx->state[6] += g;
    ctx->state[7] += h;
}

void sha256_init(SHA256_CTX *ctx)
{
    ctx->datalen = 0;
    ctx->bitlen = 0;
    ctx->state[0] = 0x6a09e667;
    ctx->state[1] = 0xbb67ae85;
    ctx->state[2] = 0x3c6ef372;
    ctx->state[3] = 0xa54ff53a;
    ctx->state[4] = 0x510e527f;
    ctx->state[5] = 0x9b05688c;
    ctx->state[6] = 0x1f83d9ab;
    ctx->state[7] = 0x5be0cd19;
}

void sha256_update(SHA256_CTX *ctx, const uint8_t *data, size_t len)
{
    for(uint32_t i = 0; i < len; ++i)
    {
        ctx->data[ctx->datalen] = data[i];
        ctx->datalen++;
        if(ctx->datalen == 64)
        {
            sha256_transform(ctx, ctx->data);
            ctx->bitlen += 512;
            ctx->datalen = 0;
        }
    }
}

void sha256_final(SHA256_CTX *ctx, uint8_t *hash)
{
    uint32_t i = ctx->datalen;

    // Pad whatever data is left in the buffer.
    if(ctx->datalen < 56)
    {
        ctx->data[i++] = 0x80;
        while(i < 56)
        {
            ctx->data[i++] = 0x00;
        }
    }
    else
    {
        ctx->data[i++] = 0x80;
        while(i < 64)
        {
            ctx->data[i++] = 0x00;
        }
        sha256_transform(ctx, ctx->data);
        for(size_t i = 0; i < 7; i++)
        {
            ((uint64_t*)ctx->data)[i] = 0;
        }
    }

    // Append to the padding the total message's length in bits and transform.
    ctx->bitlen += ctx->datalen << 3;
    *((uint32_t*)(ctx->data + 60)) = bswap_32((uint32_t)ctx->bitlen);
    *((uint32_t*)(ctx->data + 56)) = bswap_32((uint32_t)(ctx->bitlen >> 32));
    sha256_transform(ctx, ctx->data);

    WriteBE32(hash, ctx->state[0]);
    WriteBE32(hash + 4, ctx->state[1]);
    WriteBE32(hash + 8, ctx->state[2]);
    WriteBE32(hash + 12, ctx->state[3]);
    WriteBE32(hash + 16, ctx->state[4]);
    WriteBE32(hash + 20, ctx->state[5]);
    WriteBE32(hash + 24, ctx->state[6]);
    WriteBE32(hash + 28, ctx->state[7]);
}

void set_state(SHA256_CTX *ctx, uint32_t* state, size_t size)
{
    memcpy(ctx->state, state, 32);
    ctx->datalen = 0;
    ctx->bitlen = size << 3;
}
